This invention relates to an auxiliary power assist for vehicle steering systems wherein the manual effort or steering force requirements of the driver are maintained low under different driving conditions.
Prior art steering systems with auxiliary power assist arrangements operate to require a greater driver steering force in the deflection zone adjacent the center position as compared to the deflection zones remote from the center position of the hand steering wheel. This force characteristic serves to center the steering wheel to provide the driver with an adequate driving feel. Such a steering arrangement has been disclosed, for example, in U.S. Pat. No. 3,180,233.
One of the disadvantages of such prior steering systems is the higher steering effort required during parking maneuvers at a very low speed.
It is therefore an important object of the present invention to provide a steering system of the aforementioned type wherein the increased manual steering effort required during low speed operations such as parking, is reduced despite the high steering resistance of the wheels of the vehicle, and wherein the manual steering force required at the hand steering wheel during higher speed operations nevertheless increases sharply with increasing steering resistance.
In the steering system disclosed in U.S. Pat. No. 3,833,081, the steering force increases with the speed of the vehicle because of a liquid pressure output of a second special pump, said output rising proportionally to the speed of the vehicle. As a result of such an arrangement only a small manual force is required during low speed travel. The provision of a special pump involves however, an undesirable high cost for construction and installation. It is therefore an additional object of the present invention is to provide a more desirable manual force characteristic without the use of additional pumps.